Lutetium based oxyorthosilicate scintillators codoped with transition metals

ABSTRACT

Codoped lutetium-based oxyorthosilicate scintillators (e.g., lutetium oxyorthosilicase (LSO) and lutetium-ytrrium oxyorthosilicate (LYSO) scintillators) codoped with transition metal ions (e.g., Cu 2+ ) are described. The codoping can alter one or more optical and/or scintillation property of the scintillator material. For example, the codoping can increase scintillation light yield and/or decrease scintillation decay time. Radiation detectors comprising the scintillators, methods of detecting high energy radiation using the radiation detectors, and methods of altering one or more scintillation and/or optical properties of a lutetium-based oxyorthosilicate scintillator are also described.

RELATED APPLICATIONS

This application is a continuation of U.S. Pat. Application Serial No.16/839,835, filed Apr. 3, 2020, which claims the benefit of and priorityto U.S. Provisional Pat. Application Serial No. 62/830,081, filed Apr.5, 2019; the disclosures of each of which are incorporated herein byreference in their entireties.

PARTIES TO A JOINT RESEARCH AGREEMENT

The subject matter disclosed herein was made by, on behalf of, and/or inconnection with one or more of the following parties to a joint researchagreement: Siemens Medical Solutions USA, Inc., and The University ofTennessee. The agreement was in effect on and before the effectivefiling date of the presently disclosed subject matter, and the presentlydisclosed subject matter was made as a result of activities undertakenwithin the scope of the agreement.

TECHNICAL FIELD

The presently disclosed subject matter relates to methods of alteringthe optical and/or scintillation properties of lutetium basedoxyorthosilicate scintillators, such as lutetium oxyorthosilicate (LSO)and lutetium-yttrium oxyorthosilicate (LYSO), and to lutetium basedoxyorthosilicate scintillators that are codoped with transition metalions. The presently disclosed subject matter further relates toradiation detectors comprising the scintillator materials and to methodsof using the scintillator materials to detect radiation.

ABBREVIATIONS % = percentage °C = degrees Celsius at% = atomicpercentage Ca = calcium Ce = cerium cm = centimeters cm⁻¹ = inversecentimeters Cs = cesium CT = computed tomography Cu = copper Cz =Czochralski g = grams K = Kelvin keV = kiloelectron volts LSO = lutetiumoxyorthosilicate Lu = lutetium LY = light yield LYSO = lutetium-yttriumoxyorthosilicate MeV = megaelectronvolt Mg = magnesium mm = millimetermol% = mole percent nm = nanometer ns = nanoseconds PET = positronemission tomography ph = photons PL = photoluminescence PLE =photoluminescence excitation pm = picometers PMT = photomultiplier tubeppm = parts-per-million RL = radioluminescence TL = thermoluminescenceTOF = time-of-flight UV = ultraviolet Y = yttrium

BACKGROUND

Scintillator materials, which emit light pulses in response to impingingradiation, such as X-rays, gamma rays, and thermal neutron radiation,are used in detectors that have a wide range of applications in medicalimaging, particle physics, geological exploration, security and otherrelated areas. Considerations in selecting scintillator materialstypically include, but are not limited to, luminosity, decay time,energy resolution, and emission wavelength.

Lutetium oxyorthosilicate (LSO, Lu₂SiO₅) activated with cerium (Ce³⁺) isa crystal scintillator material that has been used for medical imaging,such as gamma-ray detection in positron emission tomography (PET), aswell as other applications. Due at least partly to its relatively highlight yield and short decay time, LSO is considered to be a suitablematerial for molecular imaging applications, particularly fortime-of-flight PET (TOF PET). LSO scintillators are typically made ofsingle-crystal LSO grown from a melt using, for example, the Czochralskiprocess.

While LSO scintillators in general have been developed, there is anongoing need to develop LSO and other lutetium (Lu)-basedoxyorthosilicate scintillators with improved properties for particularapplications.

SUMMARY

This summary lists several embodiments of the presently disclosedsubject matter, and in many cases lists variations and permutations ofthese embodiments. This summary is merely exemplary of the numerous andvaried embodiments. Mention of one or more representative features of agiven embodiment is likewise exemplary. Such an embodiment can typicallyexist with or without the feature(s) mentioned; likewise, those featurescan be applied to other embodiments of the presently disclosed subjectmatter, whether listed in this summary or not. To avoid excessiverepetition, this Summary does not list or suggest all possiblecombinations of such features.

In some embodiments, the presently disclosed subject matter provides ascintillator material comprising:

wherein: 0 ≤ x ≤ 1; 0 ≤ y ≤ 0.1; 0.0003 ≤ z ≤ 0.05; M is one or more ortwo or more of Ce, Pr, Nd, Sm, Eu, Tb and Yb; and M′ is one or more ortwo or more transition metal element ions selected from the groupcomprising Cr, Mn, Fe, Co, Ni, Cu, Tc, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt,and Au. In some embodiments, the scintillator material is a singlecrystal, polycrystalline, or a ceramic material. In some embodiments,0.0005≤z≤0.005. In some embodiments, 0.001≤z≤0.003. In some embodiments,M′ is Cu.

In some embodiments, 0<y≤0.1. In some embodiments, 0.0005≤y≤0.01. Insome embodiments, y is 0.001. In some embodiments, M comprises Ce andthe scintillator material is Ce⁴⁺ free.

In some embodiments, x is 0 and the scintillator material is LSO:0.1%Ce, 0.1%Cu or LSO:0.1%Ce, 0.3%Cu.

In some embodiments, the scintillator material has a light yield ofgreater than 33,000 photons per megaelectronvolt (ph/MeV). In someembodiments, the scintillator material has a light yield of greater than37,000 ph/MeV. In some embodiments, the scintillator material has alight yield of about 38,800 ph/MeV. In some embodiments, thescintillator material has an energy resolution of about 9 percent (%) orless at 662 kiloelectronvolts (keV). In some embodiments, thescintillator material has a photoluminescence decay time of about 34nanoseconds or less. In some embodiments, the scintillator material hasa scintillation decay time of about 44 nanoseconds or less. In someembodiments, the scintillator material has an afterglow that is reducedby about 50% or more compared to the non-codoped scintillator.

In some embodiments, the presently disclosed subject matter provides aradiation detector comprising a scintillator material comprising:

wherein: 0 ≤ x ≤ 1; 0 ≤ y ≤ 0.1; 0.0003 ≤ z ≤ 0.05; M is one or more ortwo or more of Ce, Pr, Nd, Sm, Eu, Tb and Yb; and M′ is one or more ortwo or more transition metal element ions selected from the groupcomprising Cr, Mn, Fe, Co, Ni, Cu, Tc, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt,and Au. In some embodiments, the detector is a medical diagnosticdevice, a device for oil exploration, and/or a device for container,vehicle, human, animal, or baggage scanning. In some embodiments, themedical diagnostic device is a positron emission tomography (PET)device, a single photon emission computed tomography (SPECT) device or aplanar nuclear medical imaging device. In some embodiments, thepresently disclosed subject matter provides a method of detecting gammarays, X-rays, cosmic rays, and particles having an energy of 1 keV orgreater, the method comprising using the radiation detector.

In some embodiments, the presently disclosed subject matter provides acodoped lutetium oxyorthosilicate (LSO) or lutetium-yttriumoxyorthosilicate (LYSO) scintillator material, wherein said scintillatormaterial has one or more property selected from the group comprising alight yield of greater than 33,000 photons per megaelectronvolt(ph/MeV), an energy resolution of about 9 percent (%) or less at 662kiloelectronvolts (keV), a photoluminescence decay time of about 34nanoseconds or less, a scintillation decay time of about 44 nanosecondsor less, and an afterglow that is reduced by about 50% or more comparedto the non-codoped scintillator. In some embodiments, said scintillatormaterial has a light yield of greater than 37,000 ph/MeV. In someembodiments, said scintillator material has a light yield of about38,800 ph/MeV.

In some embodiments, the presently disclosed subject matter provides aradiation detector comprising a codoped lutetium oxyorthosilicate (LSO)or lutetium-yttrium oxyorthosilicate (LYSO) scintillator material,wherein said scintillator material has one or more property selectedfrom the group comprising a light yield of greater than 33,000 photonsper megaelectronvolt (ph/MeV), an energy resolution of about 9 percent(%) or less at 662 kiloelectronvolts (keV), a photoluminescence decaytime of about 34 nanoseconds or less, a scintillation decay time ofabout 44 nanoseconds or less, and an afterglow that is reduced by about50% or more compared to the non-codoped scintillator. In someembodiments, the detector is a medical diagnostic device, a device foroil exploration, and/or a device for container, vehicle, human, animal,or baggage scanning. In some embodiments, the medical diagnostic deviceis a positron emission tomography (PET) device, a single photon emissioncomputed tomography (SPECT) device or a planar nuclear medical imagingdevice. In some embodiments, the presently disclosed subject matterprovides a method of detecting gamma rays, X-rays, cosmic rays, andparticles having an energy of 1 keV or greater, the method comprisingusing the radiation detector.

In some embodiments, the presently disclosed subject matter provides amethod of altering one or more scintillation and/or optical propertiesof a LSO or a LYSO scintillator, the method comprising preparing thescintillator in the presence of a dopant ion and a codopant ion, andwherein the codopant ion is one or more or two or more transition metalelement ions selected from Cr, Mn, Fe, Co, Ni, Cu, Tc, Ru, Rh, Pd, Ag,Re, Os, Ir, Pt, Au, and combinations thereof, and wherein the one ormore or two or more transition metal element ions are present at between30 ppm and 5000 ppm with respect to all cations. In some embodiments,preparing the scintillator in the presence of the dopant ion and thecodopant ion provides a scintillator with one or more of the alteredproperties selected from the group comprising increased scintillationlight yield, decreased scintillation decay time, decreased afterglow,and increased energy resolution as compared to a scintillator preparedin the presence of the dopant ion and in the absence of the codopantion.

In some embodiments, the codopant ion is Cu. In some embodiments, thedopant ion comprises Ce and the scintillator material is free of Ce⁴⁺.

It is an object of the presently disclosed subject matter to providetransition metal element codoped lutetium-based (e.g., LSO or LYSO)oxyorthosilicate scintillator materials, radiation detectors comprisingthe codoped scintillator materials, methods of using the radiationdetectors, and methods of altering the scintillator and/or opticalproperties of the scintillator materials.

An object of the presently disclosed subject matter having been statedhereinabove, and which is achieved in whole or in part by the presentlydisclosed subject matter, other objects will become evident upon areview of the description and as the description proceeds when taken inconnection with the accompanying drawings and examples as best describedherein below.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is a graph showing the maximum extraction force (measured ingrams) required to separate copper (Cu²⁺)-codoped, cerium (Ce)-dopedlutetium oxyorthosilicate (LSO) boules comprising differentconcentrations of codopant (as indicated in the x-axis) from the melt,as well as results for non-codoped and 0.1, 0.3, and 0.4 atomicpercentage (at%) calcium (Ca²⁺)-codoped Ce-doped LSO previouslypublished in Spurrier et al., J. Cryst. Growth 2008, 310, 2110-2114.Data for the Cu²⁺-codoped materials is shown in circles, data for theCa²⁺-codoped materials is shown in stars, and data for the non-codopedmaterial is shown with a square.

FIG. 2 is a graph showing the optical absorption spectra (absorptioncoefficient in inverse centimeters (cm⁻¹) versus wavelength (innanometers (nm))) of non-codoped, cerium(Ce)-doped lutetiumoxyorthosilicate (LSO:Ce, dotted line), 0.1 atomic percent (at%) copper(Cu)-codoped LSO:Ce (LSO:Ce,0.1 at%Cu, solid line), and 0.3 at%Cu-codoped LSO:Ce (LSO:Ce,0.3 at%Cu, dashed line) single crystals. Theoptical absorption spectra of non-codoped LSO:Ce (LSO:Ce, dotted line),0.1 at% calcium(Ca)-codoped LSO:Ce (LSO:Ce,0.1 %Ca, solid line), and 0.3at% Ca-codoped LSO:Ce (LSO:Ce,0.3%Ca, dashed line) single crystals areshown in the inset for comparison.

FIG. 3A is a pair of graphs showing the normalized photoluminescenceemission (PL) and photoluminescence excitation (PLE) spectra (normalizedintensity versus wavelength (in nanometers (nm)) of Ce1 (top) and Ce2(bottom) centers in a non-codoped cerium (Ce)-doped lutetiumoxyorthosilicate (LSO:Ce) material.

FIG. 3B is a pair of graphs showing the normalized photoluminescenceemission (PL) and photoluminescence excitation (PLE) spectra (normalizedintensity versus wavelength (in nanometers (nm)) of Ce1 (top) and Ce2(bottom) centers in a 0.1 atomic percent (at%) copper (Cu)-codopedcerium (Ce)-doped lutetium oxyorthosilicate (LSO:Ce) material.

FIG. 3C is a pair of graphs showing the normalized photoluminescenceemission (PL) and photoluminescence excitation (PLE) spectra (normalizedintensity versus wavelength (in nanometers (nm)) of Ce1 (top) and Ce2(bottom) centers in a 0.3 atomic percent (at%) copper (Cu)-codopedcerium (Ce)-doped lutetium oxyorthosilicate (LSO:Ce) material.

FIG. 4A is a graph showing the as measured X-ray excitedradioluminescence (RL) spectra (intensity (in arbitrary units (arb.units)) versus wavelength (nanometers (nm))) of non-codoped cerium(Ce)-doped lutetium oxyorthosilicate (LSO:Ce, squares), 0.1 atomicpercent (at%) copper (Cu)-codoped LSO:Ce (LSO:Ce, 0.1%Cu, circles), and0.3 at% Cu-codoped LSO:Ce (LSO:Ce,0.3%Cu, triangles).

FIG. 4B is a graph showing the normalized X-ray excitedradioluminescence (RL) spectra (normalized intensity versus wavelength(nanometers (nm))) of non-codoped cerium (Ce)-doped lutetiumoxyorthosilicate (LSO:Ce, squares), 0.1 atomic percent (at%) copper(Cu)-codoped LSO:Ce (LSO:Ce, 0.1%Cu, circles), and 0.3 at% Cu-codopedLSO:Ce (LSO:Ce,0.3%Cu, triangles).

FIG. 5A is a graph showing the photoluminescence (PL) decay curves(normalized intensity versus time (in nanoseconds (ns))) of Ce1 centersin non-codoped, cerium (Ce)-doped lutetium oxyorthosilicate (LSO:Ce,circles), a 0.1 atomic percent (at%) copper (Cu)-codoped LSO:Ce(LSO:Ce,0.1at%Cu, squares), and 0.3 at% Cu-codoped LSO:Ce(LSO:Ce,0.3at%Cu, diamonds). The excitation wavelength is 360 nanometers(nm) and the emission wavelength is 392 nm. The decay time of LSO:Ce was35.0 ns, the decay time of LSO:Ce,0.1at%Cu was 34.0 ns, and the decaytime of LSO:Ce,0.3at%Cu was 29.6 ns.

FIG. 5B is a graph showing the photoluminescence (PL) decay curves(normalized intensity versus time (in nanoseconds (ns))) of Ce2 centersin non-codoped, cerium (Ce)-doped lutetium oxyorthosilicate (LSO:Ce,circles), a 0.1 atomic percent (at%) copper (Cu)-codoped LSO:Ce(LSO:Ce,0.1at%Cu, squares), and 0.3 at% Cu-codoped LSO:Ce(LSO:Ce,0.3at%Cu, diamonds). The excitation wavelength is 333 nanometers(nm) and the emission wavelength is 500 nm. The decay time of LSO:Ce was46.4 ns, the decay time of LSO:Ce,0.1at%Cu was 44.7 ns, and the decaytime of LSO:Ce,0.3at%Cu was 31.7 ns.

FIG. 6 is a graph of the cesium-137 (¹³⁷Cs) pulse height spectra (counts(in arbitrary units (arb. units)) versus channel number) of 5 cubicmillimeter (mm³) single crystals of non-codoped, cerium (Ce)-dopedlutetium oxyorthosilicate (LSO:Ce), 0.1 atomic percent (at%) copper(Cu)-codoped LSO:Ce (LSO:Ce,0.1%Cu), and 0.3 at% Cu-codoped LSO:Ce(LSO:Ce,0.3%Cu). The light yield of LSO:Ce was 32,200 photons permegaelectronvolt (ph/MeV), the light yield of LSO:Ce,0.1%Cu was 38,800ph/MeV, and the light yield of LSO:Ce,0.3%Cu was 18,000 ph/MeV.

FIG. 7 is a pair of graphs of the cesium-137 (¹³⁷Cs) pulse heightspectra (counts (in arbitrary units (arb. units)) versus energy(kiloelectron volts (keV))) obtained for energy resolution (ΔE/E)evaluation of 5 cubic millimeter (mm³) single crystals of non-codoped,cerium (Ce)-doped lutetium oxyorthosilicate (LSO:Ce, top) and 0.1 atomicpercent (at%) copper (Cu)-codoped LSO:Ce (LSO:Ce,0.1%Cu, bottom). Energyresolution improves slightly, from 10% to 9% for the codoped material.

FIG. 8 is a graph showing the scintillation decay profiles (normalizedintensity versus time (in nanoseconds (ns))) of 5 cubic millimeter (mm³)single crystals of non-codoped, cerium (Ce)-doped lutetiumoxyorthosilicate (LSO:Ce, circles), 0.1 atomic percent (at%) copper(Cu)-codoped LSO:Ce (LSO:Ce,0.1%Cu, diamonds), and 0.3 at% Cu-codopedLSO:Ce (LSO:Ce,0.3%Cu, hexagons). The scintillation decay time of LSO:Cewas 45.5 ns, the scintillation decay time of LSO:Ce,0.1%Cu was 43.2 ns,and the scintillation decay time of LSO:Ce,0.3%Cu was 34.0 ns.

FIG. 9A is a graph showing the thermoluminescence (TL) glow curves (TLintensity (in arbitrary units (arb. units) versus temperature (in Kelvin(K))) of single crystals of non-codoped, cerium (Ce)-doped lutetiumoxyorthosilicate (LSO:Ce, solid line), 0.1 atomic percent (at%) copper(Cu)-codoped LSO:Ce (LSO:Ce,0.1%Cu, dashed line), and 0.3 at% Cu-codopedLSO:Ce (LSO:Ce,0.3%Cu, dotted line).

FIG. 9B is a graph showing the as-measured (heavy lines) and cumulativefitting (dashed lines) curves (TL intensity (in arbitrary units (arb.units) versus temperature (in Kelvin (K))) of single crystals ofnon-codoped, cerium (Ce)-doped lutetium oxyorthosilicate (LSO:Ce, top),0.1 atomic percent (at%) copper (Cu)-codoped LSO:Ce (LSO:Ce,0.1%Cu,middle), and 0.3 at% Cu-codoped LSO:Ce (LSO:Ce,0.3%Cu, bottom).

FIG. 10 is a graph showing the X-ray induced afterglow profiles(afterglow percent (%) versus time (in seconds (s))) of single crystalsof non-codoped, cerium (Ce)-doped lutetium oxyorthosilicate (LSO:Ce),0.1 atomic percent (at%) copper (Cu)-codoped LSO:Ce (LSO:Ce,0.1%Cu), and0.3 at% Cu-codoped LSO:Ce (LSO:Ce,0.3%Cu). Inset are images of theas-grown boule codoped with 0.3 at% Cu under UV irradiation and after UVexcitation cut-off for one minute.

FIG. 11 is a schematic drawing of an apparatus for detecting radiationaccording to the presently disclosed subject matter. Apparatus 10includes photon detector 12 optically coupled to scintillator material14. Apparatus 10 can optionally include electronics 16 for recordingand/or displaying electronic signal from photon detector 12. Thus,optional electronics 16 can be in electronic communication with photondetector 12.

DETAILED DESCRIPTION

The presently disclosed subject matter will now be described more fully.The presently disclosed subject matter can, however, be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein below and in the accompanying Examples.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of theembodiments to those skilled in the art.

All references listed herein, including but not limited to all patents,patent applications and publications thereof, and scientific journalarticles, are incorporated herein by reference in their entireties tothe extent that they supplement, explain, provide a background for, orteach methodology, techniques, and/or compositions employed herein.

I.Definitions

While the following terms are believed to be well understood by one ofordinary skill in the art, the following definitions are set forth tofacilitate explanation of the presently disclosed subject matter.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which the presently disclosed subject matter belongs.

Following long-standing patent law convention, the terms “a”, “an”, and“the” refer to “one or more” when used in this application, includingthe claims.

The term “and/or” when used in describing two or more items orconditions, refers to situations where all named items or conditions arepresent or applicable, or to situations wherein only one (or less thanall) of the items or conditions is present or applicable.

The use of the term “or” in the claims is used to mean “and/or” unlessexplicitly indicated to refer to alternatives only or the alternativesare mutually exclusive, although the disclosure supports a definitionthat refers to only alternatives and “and/or.” As used herein “another”can mean at least a second or more.

The term “comprising”, which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the namedelements are essential, but other elements can be added and still form aconstruct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”appears in a clause of the body of a claim, rather than immediatelyfollowing the preamble, it limits only the element set forth in thatclause; other elements are not excluded from the claim as a whole.

As used herein, the phrase “consisting essentially of” limits the scopeof a claim to the specified materials or steps, plus those that do notmaterially affect the basic and novel characteristic(s) of the claimedsubject matter.

With respect to the terms “comprising”, “consisting of”, and “consistingessentially of”, where one of these three terms is used herein, thepresently disclosed and claimed subject matter can include the use ofeither of the other two terms.

Unless otherwise indicated, all numbers expressing quantities of time,temperature, light output, atomic (at) or mole (mol) percentage (%), andso forth used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thisspecification and attached claims are approximations that can varydepending upon the desired properties sought to be obtained by thepresently disclosed subject matter.

As used herein, the term “about”, when referring to a value is meant toencompass variations of in one example ±20% or ±10%, in another example±5%, in another example ±1%, and in still another example ±0.1% from thespecified amount, as such variations are appropriate to perform thedisclosed methods.

The term “scintillator” refers to a material that emits light (e.g.,visible light) in response to stimulation by high energy radiation(e.g., X, α, β, or γ radiation).

The term “phosphor” as used herein refers to a material that emits light(e.g., visible light) in response to irradiation with electromagnetic orparticle radiation.

In some embodiments, the compositional formula expression of an opticalmaterial (e.g., a scintillation material or a phosphor) can contain acolon “:”, wherein the composition of the main or base matrix material(e.g., the main Lu-based oxyorthosilicate matrix) is indicated on theleft side of the colon, and the activator (or dopant ion) or theactivator and the codopant ion are indicated on the right side of thecolon. In some embodiments, the dopant and codopant can replace part ofthe Lu or other rare earth metal element(s) (e.g., Y) in a Lu-basedoxyorthosilicate scintillator material. For example,Lu₂SiO₅:0.1Ce,0.1Cu; Lu₂SiO₅:0.1%Ce,0.1%Cu; and Lu₂SiO₅:Ce³⁺ 0.1%, Cu²⁺0.1 % each represent a lutetium oxyorthosilicate optical materialactivated by cerium and codoped with copper, wherein 0.1 atomic % of thelutetium is replaced by cerium and 0.1 atomic % of the lutetium isreplaced by copper. Thus, in some embodiments, the atomic % of a dopantcan be expressed as the atomic % relative to the total amount of dopantand lutetium (or lutetium and yttrium; or dopant, Lu (or Lu and Y) andcodopant) in the base material. The atomic % of the codopant ion can beexpressed as the atomic or mole % relative to the total amount of Lu, Y,dopant and codopant.

The term “high energy radiation” can refer to electromagnetic radiationhaving energy higher than that of ultraviolet radiation, including, butnot limited to X radiation (i.e., X-ray radiation), alpha (α) particles,gamma (γ) radiation, and beta (β) radiation. In some embodiments, thehigh energy radiation refers to gamma rays, cosmic rays, X-rays, and/orparticles having an energy of 1 keV or greater. Scintillator materialsas described herein can be used as components of radiation detectors inapparatuses such as counters, image intensifiers, and computedtomography (CT) scanners.

“Optical coupling” as used herein refers to a physical coupling betweena scintillator and a photosensor, e.g., via the presence of opticalgrease or another optical coupling compound (or index matching compound)that bridges the gap between the scintillator and the photosensor. Inaddition to optical grease, optical coupling compounds can include, forexample, liquids, oils and gels.

“Light output” can refer to the number of light photons produced perunit energy deposited, e.g., by a gamma ray being absorbed, typicallythe number of light photons/MeV.

As used herein, chemical ions can be represented simply by theirchemical element symbols alone (e.g., Pr for praseodymium ion(s) (e.g.,Pr³⁺) or Cu for copper ion(s) (e.g., Cu⁺ or Cu²⁺)). Similarly, the term“transition metal element” is used herein to refer to a transition metalelement ion or a combination of transition metal element ions.

The term “transition metal element” as used herein refers to one or moreelements selected Group IIIB, IVB, VB, VIB, VIIB, VIIIB, or IB of thePeriodic Table. In some embodiments, transition metals include titanium(Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt(Co), nickel (Ni), copper (Cu), zirconium (Zr), niobium (Nb), technetium(Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), hafnium(Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium(Ir), platinum (Pt), gold (Au), rutherfordium (Rf), dubnium (Db),seborgium (Sg), bohrium (Bh), hassium (Hs), meitnerium (Mt),darmstadtium (Ds), and roentgenium (Rg). In some embodiments, thetransition metal element of the presently disclosed subject matter isnot Ti, Zr, Hf, V, Nb, Ta, Mo or W.

The term “rare earth element” as used herein refers to one or moreelements selected from a lanthanide (e.g., lanthanum (La), cerium (Ce),praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm),europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium(Ho) erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu)),scandium (Sc), and yttrium (Y).

II. Transition Element-Codoped Lutetium-Based Oxyorthosilicates

Single crystals of Ce-doped LSO are commonly used in PET scannersbecause of their high density of 7.4 g/cm³, high light yield of 75% thatof Nal:TI, and fast scintillation decay of about 40 ns. See MelcherandSchweitzer, IEEE Trans. Nucl. Sci. 1992, 39(4), 502-505; and Melcheretal., IEEE Trans. Nucl. Sci. 2003, 50(4), 762-766. Looking towardbettertiming resolution forTOF-PET applications, LSO scintillationyield, rise time and decay time have been improved by divalent codopingwith alkaline earth metal ions (e.g., Ca²⁺ or Mg²⁺ ions). See Spurrieret al., IEEE Trans. Nucl. Sci. 2008, 55, 1178-1182; and Blahuta et al.,IEEE Trans. Nucl. Sci. 2013, 60(4), 3134-3141. The increased light yieldand shortened scintillation decay time were ascribed to the suppressionof the defects that trap electrons and holes (see Yang et al., IEEETrans. Nucl. Sci. 2009, 56(5), 2960-2965) and the introduction of stableCe⁴⁺ ions (see Blahuta et al., IEEE Trans. Nucl. Sci. 2013, 60(4),3134-3141), respectively. Nonetheless, Ca²⁺ codoping was found to lowerthe surface tension of the LSO melt, and when the Ca²⁺ codopingconcentration in the melt reaches 0.4 at% the solid-liquid interface canbecome unstable, resulting in an acentric (or off-axis) growth. SeeSpurrier et al., J. Cryst. Growth 2008, 310, 2110-2114. The acentricgrowth leads to an inhomogeneous distribution of optical andscintillation performance along the radial direction (see Wu et al., J.Cryst. Growth 2018, 498, 362-371) and a decrease of crystal yield. UsingZn²⁺ as a codopant, it is possible to restore the growth stability byincreasing the surface tension of the melt. See Spurrier et al., J.Cryst. Growth 2008, 310, 2110-2114.

Zagumennyi and coworkers have reported that codoping lutetium-basedoxyorthosilicates with Cu can reduce crystal cracking as well as createwaveguide properties. See U.S. Pat. No. 6,278,832. However, they alsoreported that Cu impurities are likely to introduce Ce⁴⁺ ions inlutetium-based orthosilicates, and they describe Cu as a potentiallyharmful and undesirable impurity that results in reduced scintillationlight output. In particular, they reported that Cu impurities should becontrolled to under 30 ppm. See WO 2013/152434; U.S. Pat. ApplicationPublication No. 2014/0061537; and U.S. Pat. Application Publication No.2014/0291580. Contrary to that recommendation, the presently disclosedsubject matter is based on the finding of several beneficial effects ofdivalent Cu codoping at a much higher concentration (e.g., at 0.1 -0.2%), including simultaneous improvement of light yield, energyresolution, scintillation decay, and afterglow in LSO:Ce single crystalswithout destabilizing the solid-liquid interface or promoting acentricgrowth.

In some embodiments, the presently disclosed subject matter provides amethod of tailoring the optical and/or scintillation properties (e.g.,scintillation light yield, scintillation decay time, afterglow, risetime, energy resolution, proportionality, and sensitivity to lightexposure) of Lu-based oxyorthosilicate scintillators (e.g., LSO andlutetium-yttrium oxyorthosilicate (LYSO) scintillators) to meet theparticular needs of different applications. More particularly, in someembodiments, the presently disclosed subject matter relates to a methodof altering one or more optical and/or scintillation property of aLu-based oxyorthosilicate scintillator wherein the method comprisescodoping the scintillator with at least one type of transition metalelement ion at a molar ratio of between about 30 ppm and about 5000 ppm,between about 50 ppm and about 500 ppm, between about 90 ppm and about300 ppm, or between about 100 ppm and about 300 ppm with respect to allcations. In some embodiments, the method comprises codoping thescintillator with at least one type of transition metal element ion at amolar ratio of between about 95 ppm and about 250 ppm (e.g., 95, 100,125, 150, 175, 200, 225 or 250 ppm) or between about 100 ppm and about200 ppm with respect to all cations.

In some embodiments, the transition metal ion is not one of Ti, Zr, Hf,V, Nb, Ta, Mo, or W. In some embodiments, the transition metal ion isone or more or two or more of Cr, Mn, Fe, Co, Ni, Cu, Tc, Ru, Rh, Pd,Ag, Re, Os, Ir, Pt and Au. In some embodiments, the transition metal isCu or a mixture of Cu and another transition metal.

In some embodiments, the material does not comprise Ce as an activatoror dopant. In some embodiments, the codoped oxyorthosilicatescintillator comprises Ce as an activator or dopant, but thescintillator is Ce⁴⁺-free and has a reduction of Ce2 emissioncontribution. In some embodiments, the method provides a scintillatormaterial comprising one or more of a modified scintillation decay time,modified afterglow, modified light yield and modified energy resolution.In some embodiments, the method provides a material with a decreasedscintillation decay time, decreased afterglow, increased light yield,and/or improved energy resolution.

The presently disclosed subject matter further relates to the codopedoxyorthosilicate scintillators themselves, and related devicescontaining the codoped oxyorthosilicate scintillators, and to methods ofusing the devices to detect X-rays, gamma rays, and neutrons.

Accordingly, in some embodiments, the presently disclosed subject matterprovides a scintillator material comprising a lutetium-basedoxyorthosilicate doped with one or more activator ion and codoped withat least one transition metal element ion. In some embodiments, thelutetium-based oxyorthosilicate is codoped with at least one transitionmetal element ion at a molar ratio of between 30 ppm and 5000 ppm withrespect to all cations.

In some embodiments, the scintillator material comprises:

wherein

-   0 ≤ x ≤ 1;-   0 ≤ y ≤ 0.1;-   0.0003 ≤ z ≤ 0.05;-   M is one or more or two or more of Ce, Pr, Nd, Sm, Eu, Tb and Yb;    and-   M′ is one or more or two or more transition metal element ions.

In some embodiments, the material is a single crystal, polycrystallineor a ceramic material. Thus, in some embodiments, x is 0 and thescintillator is an LSO scintillator. In some embodiments, x is greaterthan 0 and the scintillator is a LYSO scintillator.

In some embodiments, 0<y≤0.1. In some embodiments, 0.0005≤y≤0.01. Insome embodiments, 0.001≤y≤0.005. In some embodiments, y is about 0.001.In some embodiments, M is other than Ce (i.e., M is Pr, Nd, Sm, Eu, Tb,Yb, or a combination thereof). In some embodiments, M is Ce or Pr.

Codopant M′ can be any suitable transition metal element ion or acombination of transition metal element ions. In some embodiments, M′ isone or more or two or more of the group comprising Cr, Mn, Fe, Co, Ni,Cu, Tc, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, and Au. In some embodiments, M′comprises Cu (e.g., Cu²⁺). In some embodiments, M′ is Cu (e.g., Cu²⁺).

In some embodiments, 0.0005≤z≤0.005. In some embodiments,0.0009≤z≤0.003. In some embodiments, 0.001≤z≤0.003. In some embodiments0.001≤z≤0.002. In some embodiments, 0.00095≤z≤0.0025. In someembodiments, 0.00095≤z≤0.0015. In some embodiments, z is about 0.001.

In some embodiments, M is Ce and the scintillator material is Ce⁴⁺ free.

In some embodiments, the scintillator material comprises LSO:0.1%Ce,0.1%Cu or LSO:0.1%Ce,0.3%Cu.

In some embodiments, the scintillator material has a light yield ofgreater than about 33,000 photons per megaelectronvolt (ph/MeV) (e.g.,greater than about 33,000; 34,000; 35,000; or about 36,000 ph/MeV). Insome embodiments, the scintillator material has a light yield of greaterthan about 37,000 ph/MeV. In some embodiments, the scintillator materialhas a light yield of about 38,800 ph/MeV.

In some embodiments, the scintillator material has an energy resolutionthat is less than the energy resolution of a comparable non-codopedscintillator. In some embodiments, the scintillator has an energyresolution of about 9 percent (%) or less at 662 kiloelectronvolts(keV).

In some embodiments, the scintillator material has a shorterphotoluminescence (PL) and/or scintillation decay time than a comparablenon-codoped material. In some embodiments, the scintillator material hasa PL decay time of about 34 nanoseconds (ns) or less. In someembodiments, the scintillator material has a PL decay time of about 32ns or less (e.g., about 32, 31, or about 30 ns or less). In someembodiments, the scintillator material has a PL decay time of about 29.6ns. In some embodiments, the scintillator material has a scintillationdecay time of about 44 nanoseconds of less (e.g., about 44, 43, 42, 41,40, 39, 38, 37, 36, 35, or about 34 ns).

In some embodiments, the scintillator has an afterglow that is reducedby about 50% or more compared to the non-codoped scintillator.

Accordingly, in some embodiments, the presently disclosed subject matterprovides a codoped LSO or LYSO scintillator material, wherein saidscintillator material has one or more property selected from the groupcomprising: a light yield of greater than 33,000 photons permegaelectronvolt (ph/MeV), an energy resolution of about 9 percent (%)or less at 662 kiloelectronvolts (keV), a photoluminescence decay timeof about 34 nanoseconds or less, a scintillation decay time of about 44nanoseconds or less, and an afterglow that is reduced by about 50% ormore compared to the non-codoped scintillator.

In some embodiments, the presently disclosed subject matter provides aradiation detector comprising the codoped scintillator material asdescribed herein. For example, the radiation detector can comprise oneor more of the presently disclosed scintillator materials (which absorbradiation and emit light) and a photodetector (which detects saidemitted light). The photodetector can be any suitable detector ordetectors and can be or not be optically coupled (e.g., via opticalgrease or another optical coupling compound, such as an optical couplingoil or liquid) to the scintillator material for producing an electricalsignal in response to emission of light from the scintillator material.Suitable photon detectors include, but are not limited to,photomultiplier tubes, photodiodes, CCD sensors, and image intensifiers.Thus, the photodetector can be configured to convert photons to anelectrical signal. For example, a signal amplifier can be provided toconvert an output signal from a photodiode into a voltage signal. Thesignal amplifier can also be designed to amplify the voltage signal.Electronics associated with the photodetector can be used to shape anddigitize the electronic signal, e.g., for recording and/or displayingthe electronic signal.

Referring now to FIG. 11 , in some embodiments, the presently disclosedsubject matter provides an apparatus 10 for detecting radiation whereinthe apparatus comprises a photon detector 12 and a scintillator material14 (e.g., a lutetium based oxyorthosilicate scintillator codoped with atransition metal element ion). Scintillator material 14 can convertradiation to light that can be collected by a charge-coupled device(CCD) or a photomultiplier tube (PMT) or other photon detector 12efficiently and at a fast rate.

Referring again to FIG. 11 , photon detector 12 can be any suitabledetector or detectors and can be optically coupled (e.g., via opticalgrease or another optical coupling compound, such as an optical couplingoil or liquid) to the scintillator (e.g., the transition metal elemention codoped lutetium based oxyorthosilicate) for producing an electricalsignal in response to emission of light from the scintillator. Thus,photon detector 12 can be configured to convert photons to an electricalsignal. Electronics associated with photon detector 12 can be used toshape and digitize the electronic signal. Suitable photon detectors 12include, but are not limited to, photomultiplier tubes, photodiodes, CCDsensors, and image intensifiers. Apparatus 10 can also includeelectronics 16 for recording and/or displaying the electronic signal.

In some embodiments, the radiation detector is configured for use aspart of a medical or veterinary diagnostic device, a device for oil orother geological exploration (e.g., oil well logging probes), or as adevice for security and/or military-related purposes (e.g., as a devicefor container, vehicle, or baggage scanning or for scanning humans orother animals). In some embodiments, the medical or veterinarydiagnostic device is selected from, but not limited to, a positronemission tomography (PET) device, an X-ray computed tomography (CT)device, a single photon emission computed tomography (SPECT) device, ora planar nuclear medical imaging device. For example, the radiationdetector can be configured to move (e.g., via mechanical and/orelectronic controls) over and/or around a sample, such as a human oranimal subject, such that it can detect radiation emitted from anydesired site or sites on the sample. In some embodiments, the detectorcan be set or mounted on a rotating body to rotate the detector around asample.

In some embodiments, the device can also include a radiation source. Forinstance, an X-ray CT device of the presently disclosed subject mattercan include an X-ray source for radiating X-rays and a detector fordetecting said X-rays. In some embodiments, the device can comprise aplurality of radiation detectors. The plurality of radiation detectorscan be arranged, for example, in a cylindrical or other desired shape,for detecting radiation emitted from various positions on the surface ofa sample.

In some embodiments, the presently disclosed subject matter provides amethod for detecting radiation (or the absence of radiation) using aradiation detector comprising a scintillator as described hereinabove(e.g., a codoped oxyorthosilicate scintillator material). Thus, in someembodiments, the presently disclosed subject matter provides a method ofdetecting gamma rays, X-rays, cosmic rays and particles having an energyof 1 keV or greater, wherein the method comprises using a radiationdetector comprising a transition metal ion codoped oxyorthosilicate asdescribed herein. In some embodiments, the method can comprise providinga radiation detector comprising a photodetector and an optical (e.g.,scintillator) material of the presently disclosed subject matter;positioning the detector, wherein the positioning comprises placing thedetector in a location wherein the optical material is in the path of abeam of radiation (or the suspected path of a beam of radiation); anddetecting light (or detecting the absence of light) emitted by theoptical material with the photodetector. Detecting the light emitted bythe optical material can comprise converting photons to an electricalsignal. Detecting can also comprise processing the electrical signal toshape, digitize, or amplify the signal. The method can further comprisedisplaying the electrical signal or processed electrical signal.

The presently disclosed scintillator materials can be prepared via anysuitable method as would be apparent to one of ordinary skill in the artupon a review of the instant disclosure. In some embodiments, thepresently disclosed subject matter provides a method of preparing acodoped Lu-based oxyorthosilicate scintillator material (e.g., a codopedLSO or LYSO). In some embodiments, the presently disclosed subjectmatter provides a method for preparing a scintillator material thatcomprises preparing a crystal from a melt. In some embodiments, the meltcan be prepared from suitable starting materials (such as oxides orcarbonates, e.g., CeO₂, Lu₂O₃, SiO₂), mixed at a ratio based upon thedesired elemental content of the scintillator. In some embodiments, thecodoped Lu-based oxyorthosilicate scintillator material can be a crystalgrown by the Czochralski (pulling-up) method. However, single crystalsor polycrystalline materials and/or ceramics grown or produced by othermethods can also be used as a scintillator material according to thepresent disclosure. For example, alternative methods for producing thematerials include, but are not limited to the micro-pulling down method,Bridgman method, zone melt method, Edge-defined Film-fed Growth (EFG)method, and hot isostatic press (HIP) sintering method.

The scintillator materials can be provided as single crystals, as apolycrystalline material, and/or as a ceramic material. In someembodiments, the material is provided as a polycrystalline and/orceramic material. The polycrystalline and/or ceramic material can haveanalogous physical, optical and scintillation properties as a singlecrystal otherwise having the same chemical composition.

In some embodiments, the method further comprises annealing thescintillator material for a period of time (e.g., between a few hoursand a few days). The annealing can be performed, for example, in air,nitrogen, or a mixture of nitrogen and hydrogen. The annealing can bedone at any suitable temperature, e.g., between about 800 and about1600° C. (e.g., about 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, andabout 1600° C.).

In some embodiments, the presently disclosed subject matter provides amethod of altering one or more scintillation and/or optical propertiesof a lutetium-based oxyorthosilicate scintillator, the method comprisingpreparing the lutetium-based oxyorthosilicate scintillator in thepresence of a dopant ion and a codopant ion, and wherein the codopantion is one or more or two or more transition metal element ions. In someembodiments, the codopant ion is Cu. In some embodiments, the codopantion or ions are provided at about 5000 ppm or less with respect to allcations (e.g., Lu, Y, and dopant ion or ions). In some embodiments, thecodopant ion or ions are provided at about 30 ppm to about 5000 ppm withrespect to all cations. In some embodiments, the codopant ion or ionsare provided at about 50 to about 500 ppm, about 90 to about 300 ppm,about 100 to about 300 ppm, about 100 to about 200 ppm, or at about 100ppm with respect to all cations. In some embodiments, the codopingprovides a Ce doped Lu-based oxyorthosilicate scintillator with areduction in Ce2 emission. In some embodiments, the codoping provides aCe-doped Lu-based oxyorthosilicate scintillator that is Ce⁴⁺ free. Insome embodiments, the Lu-based oxyorthosilicate scintillator is dopedwith a dopant other than Ce.

In some embodiments, each of the one or more scintillation and/oroptical properties is selected from the group comprising scintillationlight yield, scintillation decay time, afterglow, rise time, energyresolution, proportionality, and sensitivity to light exposure. In someembodiments, each of the one or more scintillator and/or opticalproperties is selected from scintillation decay time (i.e., faster orslower scintillation decay time), afterglow (i.e., increased ordecreased afterglow), light yield (e.g., increased scintillation lightyield), and energy resolution (i.e., improved energy resolution). Insome embodiments, preparing the scintillator in the presence of thedopant ion and the codopant ion provides a scintillator with one or moreof the altered properties selected from the group comprising increasedscintillation light yield, decreased scintillation decay time, decreasedafterglow, and increased energy resolution as compared to a scintillatorprepared in the presence of the dopant ion and in the absence of thecodopant ion.

EXAMPLES

The following examples are included to further illustrate variousembodiments of the presently disclosed subject matter. However, those ofordinary skill in the art should, in light of the present disclosure,appreciate that many changes can be made in the specific embodimentswhich are disclosed and still obtain a like or similar result withoutdeparting from the spirit and scope of the presently disclosed subjectmatter.

Example 1 Crystal Growth

The Czochralski (Cz) method was used to grow LSO:0.1 at% Ce³⁺ crystalscodoped with 0, 0.1, and 0.3 at% Cu²⁺. The starting materials wereLu₂O₃, SiO₂, CeO₂, and CuO with at least 99.99% purity. The atomicpercentage of the dopant and codopant concentrations is relative to thatof lutetium in the melt. The dopant and codopant concentrations in thegrown boule will be lower than the nominal concentration in the meltbecause of the segregation that occurs during growth. The crystals weregrown in iridium crucibles which were loaded with raw materials andinductively heated by a 30 kW Hüttinger power supply (TRUMPF GmbH & Co.KG Hüttinger, Freiburg im Breisgau, Germany). The growth atmosphere wasa mixture of nitrogen and a small fraction of oxygen. All as-grownboules are 32 mm in diameter and 110 mm long. All 5 mm³ samples used formeasurements were cut from the middle section of their respectiveboules.

Example 2 Optical Property Measurements

Optical absorption spectra from 200 to 800 nm were acquired with aVarian Cary 5000 UV-VIS-IR spectrophotometer (Varian Inc., Palo Alto,California, United States of America).

Photoluminescence emission (PL) and excitation (PLE) spectra wererecorded with a HORIBA™ Jobin Yvon Fluorolog-3 spectrofluorometer (HORIBA Ltd., Kyoto, Japan). A 450 W continuous xenon lamp was used as anexcitation source. Photoluminescence decay profiles were conducted onthe same spectrofluorometer using a time-correlated-single-photoncounting module. The excitation sources are light emitting diodes(HORIBA™ Jobin Yvon NanoLEDs; HORIBA Ltd., Kyoto, Japan). The durationof the light pulse was shorter than 2 ns.

Example 3 Scintillation Performance Measurements

The scintillation decay profile was acquired with an Agilent DSO6104Adigital oscilloscope (Agilent Technologies, Santa Clara, California,United States of America) in single shot mode under ¹³⁷Cs sourceirradiation.

The scintillation light yields (LY) were evaluated using a pulseprocessing chain that consists of a Hamamatsu R2059 photomultiplier tube(PMT, Hamamastu Photonics, K.K., Hamamatsu City, Japan), an Ortec 672Amp (Advanced Measurement Technology, Inc., Oak Ridge, Tennessee, UnitedStates of America), a Canberra model 2005 pre-Amp (Canberra Industries,Ind., Meridan, Connecticut, United States of America), and a Tukan 8kmulti-channel analyzer (MCA, National Center for Nuclear Research,Świerk, Poland). A shaping time of 3 µs was used to achieve full lightintegration. Each sample was measured under irradiation with a 15 µCi¹³⁷Cs source. To maximum the light collection, mineral oil was used as acouplant between the sample and the PMT, and a 50 mm diameter PTFE-lineddome-shaped reflector was used as a top reflector. The error bar of theLY is ±5%. The energy resolutions of the samples at 662 keV wereevaluated by using a Hamamatsu R6231-100 PMT (Hamamastu Photonics, K.K.,Hamamatsu City, Japan).

X-ray radioluminescence (RL) measurements were conducted in atransmission mode under excitation of a copper x-ray source operated at35 kV and 0.1 mA. The emission signals were detected with a focal lengthmonochromator and a broadband PMT. The emission intensities werecorrected by the acquisition software based on the spectral sensitivityof the PMT.

The room temperature afterglow profiles of the samples were acquiredusing a Hamamatsu R2059 PMT (Hamamastu Photonics, K.K., Hamamatsu City,Japan) operated at -1500 V_(bias). To enhance the light collection, aTetratex® TX3104 PTFE membrane (Donaldson Company, Minneapolis,Minnesota, United States of America) was used as a reflector. Thesamples were stored in the dark for 24 hours before measurements. Thesamples irradiated with X-rays for 15 min while being held in the dark,and the emission signals from each sample were recorded immediatelyafter irradiation cut-off.

Example 4 Thermoluminescence Measurements

Thermoluminescence (TL) glow curves were acquired in the temperaturerange of 275 to 550 K. After X-ray irradiation at 275 K with an X-raytube operated at 35 kV and 0.1 mA for 15 min, the TL glow curve wasrecorded while heating the sample at a rate of 3 K/min. Prior to the TLmeasurements, the samples were individually heated to 550 K to ensurethat all traps in the temperature range were empty. A Hamamatsu R2059PMT (Hamamastu Photonics, K.K., Hamamatsu City, Japan) optically coupledto a cryostat’s borosilicate window was used to record the spectrallyunresolved emission from the sample. Standard National Institute Module(NIM) electronics were used to convert the PMT current signal into avoltage signal. The voltage signal was digitized by a NationalInstruments 6002-E data acquisition card (National Instruments, Austin,Texas, United States of America). The sample temperature and the signalintensity were correlated.

Example 5 Discussion of Examples 1-4

Stable crystal growth of Cu²⁺ codoped LSO:Ce with reduced surfacetension of the melt:

The effect of Cu²⁺ codoping on the surface tension of the LSO melt wasinvestigated by using a previously described method. See Spurrier etal., J. Cryst. Growth 2008, 310, 2110-2114. When a grown boule isextracted from the melt, the force exerted on the melt surface can beseen by an increase in the mass reading on the associated load cell;this continues to increase until reaching a maximum value. Thedifference between the initial mass reading and the maximum value can beused to make a relative comparison of the surface tension of the meltfor each composition. The surface tension is proportional to the maximumforce required to extract the boule from the melt. See KSV INSTRUMENTSLTD., “Surface and interfacial tension”, Application Note #101. Themaximum extraction forces for 0.1 and 0.3 at% Cu²⁺ codoped LSO:Ce boulesare plotted in FIG. 1 , as well as the published values for non-codoped,0.1, 0.3, and 0.4 at% Ca²⁺ codoped LSO:Ce for comparison. The surfacetension of the Cu²⁺ codoped LSO:Ce melt is lower than that ofnon-codoped one, but still higher than that of Ca²⁺ codoped ones withequivalent codopant concentration in the melt. The as-grown LSO:Ceboules codoped with 0.1 and 0.3 at% Cu²⁺ are not only highly transparentand almost crack-free, but also without any tendency toward acentricgrowth. Without being bound to any one theory, these observationsindicate that the reduced surface tension induced by Cu²⁺ codoping isnot large enough to cause growth instability.

Ce Valence State: Non-Conversion of Stable Ce³⁺ to Ce⁴⁺

Optical absorption spectroscopy is a qualitative tool to identify thepresence of stable Ce⁴⁺ ions in Ce doped oxides due to the detectableligand-to-metal charge transfer (CT) transition of Ce⁴⁺. See Blahuta etal., IEEE Trans. Nucl. Sci. 2013, 60(4), 3134-3141; Wu etal., Phys. Rev.Appl. 2014, 2 044009, 1-13; Nikl et al., Cryst. Growth Des. 2014, 14,4827-4833; Liu et al., Phys. Status Solidi RRL, 2014, 8, 105-109; andChewpraditkul et al., Opt. Mater. 2013, 35, 1679-1684. Because of thepartial conversion of stable Ce³⁺ into Ce⁴⁺ ions in an LSO (or LYSO)host induced by divalent Ca and Mg codoping (see Blahuta et al., IEEETrans. Nucl. Sci. 2013, 60(4), 3134-3141; and Chewpraditkul et al., Opt.Mater. 2013, 35, 1679-1684), and the importance of stable Ce⁴⁺ fortiming properties (see Kochurikhin et al., J. Crystal Growth 1996, 160,181-183; Nikl et al., Cryst. Growth Des. 2014, 14, 4827-4833; and Liu etal., Phys. Status Solidi RRL, 2014, 8, 105-109), the effect of divalentCu codoping on the Ce valence state was investigated. As seen in FIG. 2, the spectrum of non-codoped LSO:Ce shows typical Ce³⁺ 4f-5dabsorptions. The Ce oxidation state in Cz-grown LSO:Ce single crystalshas been proven to be purely trivalent by both X-ray absorptionspectroscopy and electron energy loss spectroscopy. See Melcher et al.,IEEE Trans. Nucl. Sci. 2005, 52, 1809-1812; and Wu et al., Phys. StatusSolidi RRL2019, 13, 1800472 1-5. The spectra of Cu²⁺ codoped LSO:Cesamples, regardless of Cu²⁺ concentration, also show the Ce³⁺ 4f-5dabsorptions without the presence of CT absorption band of Ce⁴⁺. Thisindicates that the stable Ce³⁺ will not be converted into Ce⁴⁺ with Cu²⁺codoping, dissimilar to the effect of Cu⁺ (see U.S. Pat. No. 6,278,832)and Ca²⁺ codoping (see FIG. 2 inset). See Spurrier et al., IEEE Trans.Nucl. Sci. 2008, 55, 1178-1182; and Blahuta et al., IEEE Trans Nucl.Sci. 2013, 60(4), 3134-3141. The Cu valence state in LSO is expected tomaintain +2 or reach a higher valence state (+3 or +4) rather than +1;because, since the Cu atoms coordinate with highly electronegativeoxygen atoms in the LSO host lattice, there should be enough electronaffinity and electrostatic attraction to draw off 3d valenceelectron(s).

Luminescence Characteristics of Ce1 and Ce2 Centers: The Suppression ofCe2 Emission and an Enhanced Ionization of the Ce³⁺ 5d₁ State

In the LSO host lattice, Ce ions are known to occupy two different Lusites. Ce1 is usually designated to the Lu site neighboring to sevenoxygens, and Ce2 is designated to the Lu site neighboring to sixoxygens. See Cooke et al., Phys. Rev. B 2000, 61, 11973-11978; and Ninget al., J. Mater. Chem. 2012, 22 13723-13731. Ce1 and Ce2 centers havedistinct spectral properties and decay kinetics. The Ce³⁺ 5d-4femissions of Ce1 centers are at 3.15 and 2.9 eV with a PL decay of 33ns, and 2.64 eV for Ce2 centers with a PL decay of 46 ns. See Jary etal., Opt. Mater. 2011, 34, 428-432; and Ding et al., J. Solid StateChem. 2014, 209, 56-62. The PL, PLE, and RL spectra, and PL decays wereused to study the effects of Cu²⁺ codoping on the luminescencecharacteristics of Ce1 and Ce2 centers.

FIGS. 3A-3C show the normalized PL and PLE spectra of Ce1 and Ce2centers in non-codoped and Cu²⁺ codoped LSO:Ce. All the emission spectracan be well fitted with three Gaussian peaks with maximums at 3.15 eV(393 nm), 2.91 eV (426 nm), and 2.64 eV (470 nm). See Jary et al., Opt.Mater. 2011, 34, 428-432; and Ding et al., J. Solid State Chem. 2014,209, 56-62. The two peaks at 2.91 and 3.15 are Ce1 emissions, and thepeak at 2.64 eV is Ce2 emission. As the Cu²⁺ codoping concentrationincreases, the emission contribution from Ce2 centers graduallydecreases. It should be noted that monovalent Li codoping can alsoreduce the emission contribution from Ce2 without formation of stableCe⁴⁺. See Wu et al., ACS Appl. Mater. Interface 2019, 11, 8194-8201. Thereduction/suppression of Ce2 emission was also observed in Ca²⁺ codopedLSO:Ce, which was attributed to the occupation of Ce2 sites by opticallyinactive Ce⁴⁺ ions instead of Ce³⁺ ions, as a result of chargecompensation due to Ca²⁺ codoping. See Wu et al., J. Cryst. Growth 2018,498, 362-371. However, this explanation does not apply to the case ofCu²⁺ codoping because no stable Ce⁴⁺ was created by Cu²⁺ codoping. Theas-measured RL spectra of non-codoped, 0.1 at%, and 0.3 at% Cu²⁺ codopedLSO:Ce are shown in FIG. 4A. A 20% increase of scintillation efficiencyof LSO:Ce is achieved by 0.1 at% Cu codoping, but it decreases when theCu concentration is further increased to 0.3 at%. The RL spectra werenormalized for a better comparison of the emission contributions fromCe1 and Ce2. See FIG. 4B. There is a reduction of emission contributionfrom Ce2, consistent with the PL emission results.

The PL decay curves of non-codoped, 0.1 at%, and 0.3 at% Cu²⁺ codopedLSO:Ce can be well fitted by a single exponential function. See FIGS. 5Aand 5B. The decay constants of both Ce1 and Ce2 emissions decrease withincreased Cu²⁺ codoping concentration. For the Ce1 emission, the decaytime decreases from 35.0 ns for non-codoped, 34.0 ns for 0.1 at% Cu, to29.6 ns for 0.3 at% Cu. See FIG. 5A. For the Ce2 emission, it decreasesfrom 46.4 ns for non-codoped, 44.7 ns for 0.1 at% Cu, to 31.7 ns for 0.3at% Cu. See FIG. 5B. Also, the background value relative to the decayamplitude increases noticeably in highly codoped samples. For LSO andLYSO, the luminescence quenching of Ce³⁺ at high temperature is causedby the thermal ionization process from the Ce³⁺ 5d₁ state to theconduction band (CB). See Kolk et al., Appl. Phys. Lett. 2003, 83,1740-1742; and Feng et al., J. Appl. Phys. 2010, 108, 033519 1-6. Theionization process can promote an electron into the CB and leave atemporary Ce⁴⁺ behind. The electron left in the CB can recombine withthe other temporary Ce⁴⁺ centers, and then result in a delayed emission.The delayed emission spreading into much longer time scales than thetime delay between two subsequent optical excitation pulses can causethe background signal to rise. The shortening of decay times of both Ce1and Ce2 emissions also implies an increased probability of non-radiativerecombination through the ionization process.

Scintillation Properties: A Simultaneous Improvement of Light Yield,Energy Resolution, and Scintillation Decay Time

Pulse height spectra of 5 mm³ non-codoped and Cu²⁺ codoped LSO:Cesamples acquired by a Hamamatsu R2059 PMT under ¹³⁷Cs gamma-ray sourceirradiation are plotted in FIG. 6 . The absolute light yield wasevaluated by using the single photoelectron method (see Moszynski etal., IEEE Trans. Nucl. Sci. 1997, 44, 1052-1061) and theemission-weighted quantum efficiency of the PMT estimated for eachsample. The light yield of the non-codoped LSO:Ce sample is 32,000photons/MeV. The light yield can be enhanced to about 39,000 photons/MeVwith 0.1 at% Cu²⁺ codoping. This result is comparable to the valuesachieved by Ca²⁺ (see Spurrier et al., IEEE Trans. Nucl. Sci. 2008, 55,1178-1182) and Li⁺ (see Wu et al., Phys. Status Solidi RRL2019, 13,1800472 1-5) codoping. As the Cu²⁺ codoping concentration is furtherincreased to 0.3 at%, the light yield drops to 18,000 photons/MeV. Thepulse height spectra acquired for energy resolution evaluation are shownin FIG. 7 . The energy resolution (ΔE/E) is calculated as the full widthat half maximum of a photopeak divided by the location of the peakcentroid. The energy resolution at 662 keV slightly improves from 10%for non-codoped to 9% for the 0.1 at% Cu²⁺ codoped sample.

The scintillation decay curves of non-codoped, 0.1, and 0.3 at% Cu²⁺codoped LSO:Ce samples are presented in FIG. 8 . All curves can be wellfit by a single exponential function. The scintillation decay time showsa monotonically decreasing trend with the increase in Cu²⁺concentration, from 45.5 ns for non-codoped, 43.2 ns for 0.1 at% Cu²⁺,to 34.0 ns for the 0.3 at% Cu²⁺ codoped sample. Without being bound toany one theory, such a scintillation decay time shortening with codopingcan be explained in an similar way as has been done in Li⁺ codopedLSO:Ce (see Wu et al., ACS Appl. Mater. Interface 2019, 11, 8194-8201),but is different from the Ce⁴⁺-involved mechanism for Ca²⁺ or Mg²⁺codoped LSO:Ce. See Blahuta et al., IEEE Trans. Nucl. Sci. 2013, 60(4),3134-3141. Specifically, it is believed that the shortening ofscintillation decay time in Cu²⁺ codoped LSO:Ce originates from thereduced PL decay time of Ce1 and Ce2 due to an enhanced thermalionization from the Ce³⁺ 5d₁ state, and the suppression of the slow Ce2emission.

Defect Structure: Thermoluminescence and Afterglow Analysis

Because of the valence state mismatch between Cu²⁺ codopants and Lu³⁺and Si⁴⁺ host cations, and the non-conversion of stable Ce³⁺ to Ce⁴⁺,the defect structure of LSO:Ce has to be altered by Cu²⁺ codoping inorder to achieve electrical neutrality in the lattice. TL as aneffective tool to detect the trap states was utilized to study theeffect of Cu²⁺ codoping on defect structure. The TL glow curves ofnon-codoped and Cu²⁺ codoped LSO:Ce are shown in FIG. 9A. Fornon-codoped LSO:Ce, the dominant TL peaks at 346, 404, 451, and 510 Kare associated with the oxygen vacancies (Vo) that are the nearestneighbors to the Ce center. See Vedda et al., Phys. Rev. B 2008, 78,195123 1-8. These TL emissions have been attributed to the radiativerecombination of electrons stored in Vo with holes localized at Ce³⁺through a thermally assisted tunneling mechanism. See Vedda et al.,Phys. Rev. B 2008, 78, 195123 1-8. A drastic decrease of the TL peak at346 K is observed in 0.1 at% Cu²⁺ codoped sample. For the 0.3 at% Cu²⁺codoped sample, although the TL peaks at 346 and 404 K are completelyreduced, two new TL peaks at 288 and 480 K appear with high emissionsignals.

Further discussion is based on a quantitative analysis of TL peaks and acomparison with the results of Ca²⁺ and Li⁺ codoping. The modifiedgeneral-order kinetics expression describing TL intensity / as afunction of temperature T (see Feng et al., J. Appl. Phys. 2008, 103,083109 1-7) is utilized to fit the glow curve:

$I(T) = sn_{0}\exp( {- \frac{E_{t}}{\kappa_{B}T}} ) \times$

$\{ {\frac{( {l - 1} )s}{\beta}\, \times \, T\, \times \,\exp( {- \frac{E_{t}}{\kappa_{B}T}} )\, \times \,\lbrack {( \frac{\kappa_{B}T}{E_{t}} )\, - \, 2( \frac{\kappa_{B}T}{E_{t}} )^{2}\, + \, 6( \frac{\kappa_{B}T}{E_{t}} )^{3}} \rbrack\, + \, 1} \}^{l/{({1 - l})}}$

where n₀ is the concentration of trapped charges at t=0, E_(t) theenergy level of the trap, κ_(B) the Boltzmann constant, / the kineticorder, s the frequency factor, and β the heating rate (3 K/min in thismeasurement). The TL parameters of LSO:Ce evaluated from the partialcleaning and initial rise method (previously published in Vedda et al.,Phys. Rev. B 2008, 78, 195123 1-8) were used as initial fittingparameters. As seen in FIG. 9B, the fitting curves agree well with theexperimental ones. The results of peak temperature, trap depth, andfrequency are listed in Table 1, below. The derived trap depth andfrequency confirm the suppression of Vo (and/or dissociation of Ce andVo) by Cu²⁺ codoping, and the introduction of new deep traps in highlycodoped samples.

TABLE 1 TL fitting parameter of non-codoped, 0.1 at%, and 0.3 at% Cu²⁺codoped LSO:Ce single crystals. Composition Peak temperature (K) Trapdepth (eV) Frequency (s⁻¹) De-trapping time (s) LSO:Ce 346 0.99 4.0×10¹²1.5×10² 404 0.99 2.5×10¹⁰ 2.4×10⁴ 451 0.99 1.0×10⁹ 6.1×10⁵ 510 0.994.0×10⁷ 1.5×10⁷ LSO:Ce,0.1at%Cu 427 1.16 5.9×10¹¹ 2.2×10⁹ 497 1.099.0×10⁸ 5.2×10⁷ LSO:Ce,0.3at%Cu 288 0.61 7.0×10⁸ 2.5×10¹ 480 2.001.7x10¹⁹ 2.4x10¹⁴

On a basis of optical properties mentioned above, Cu²⁺ and Li⁺ codopingwas found to have the same effect on Ce valence state and theluminescence properties of Ce1 and Ce2 center, but both are differentfrom Ca²⁺ codoping. Without being bound to any one theory, thesimilarity between Li⁺ and Cu²⁺ codoping can be ascribed to their closeionic radii, for example, under 6-coordination, the ionic radii of Li⁺and Cu²⁺ are 76 and 73 picometers (pm), respectively, much smaller thanthat of Ca (i.e., 100 pm). See Shannon, Acta Cryst. 1976, A32, 751-767.Ca²⁺ with a larger ionic radius is supposed to occupy theseven-coordinated Lu³⁺ site and induce the stable Ce⁴⁺ions. See Wu etal., J. Cryst. Growth 2018, 498, 362-371. In contrast, Li⁺ ions areprone to occupy not only seven-coordinated Lu³⁺ substitution sites butalso the six-coordinated interstitial spaces. See Wu et al., ACS Appl.Mater. Interface 2019, 11, 8194-8201; and Jia et al., Matt. Lett., 2018,228, 372-374. The electrical neutrality of the system can be achieved byself-compensation between Li_(i) and Li_(Lu), and the variation in typeand concentration of Vo, rather than by the conversion of Ce valencestates. See Wu et al., ACS Appl. Mater. Interface 2019, 11, 8194-8201.Thus, it is reasonable to believe that Cu²⁺ ions also tend to occupy theLu³⁺ substitutional site and the interstitial space. Moreover, the ratiobetween Cu_(Lu) and Cu_(i) should depend on the Cu²⁺ codopingconcentration, analogous to that of Li⁺ codoping. See Wu et al., ACSAppl. Mater. Interface 2019, 11, 8194-8201. Specifically, the Cu_(i)should be dominant in the lightly codoped sample, and the Cu_(Lu) isdominant in highly codoped sample. This deduction can explain the TLvariation induced by Cu²⁺ codoping: i) the dominant and positivelycharged Cu_(i) in the lightly codoped sample (0.1 at% Cu) cansuppress/diminish the formation of Vo, which leads to a drasticreduction of the TL peak at 346 K (see FIG. 9A); ii) the dominantCu_(Lu) in the highly codoped sample can couple with Vo to form{Cu_(LU)+Vo} complex defects due to the Coulomb attraction. Theformation of complex defects can dissociate the spatially-correlated Ceand Vo and result in a suppression of the four Vo-associated TL peaks(see FIG. 9A), similar to the effect of {Ca_(Lu)+Vo} complex assuggested in Ca²⁺ codoped LSO. See Wu et al., J. Cryst. Growth 2018,498, 362-371. However, there is a difference between Cu²⁺codoping andboth Li⁺ and Ca²⁺ codoping in that the newly formed defects themselves,such as Cu_(Lu) and {Cu_(Lu)+Vo}, can serve as new electron traps withan energetically depth of 0.6 and 2.0 eV. ⁶³Cu nuclear magnetic resonant(NMR) experiments and density functional theory (DFT) calculations couldbe used to clarify the preferential site occupation of Cu²⁺ ions in LSOand its role on defect structure alternation.

Based on the fitted trap parameters, the de-trapping time τ at roomtemperature (RT) was calculated by using the following equation:

τ = s⁻¹ × e^(E/kT)

See Vedda et al., Phys. Rev. B 2009, 80, 045113 1-9. The calculatedde-trapping times at RT are listed in Table 1, above. Since there is acorrelation between deep traps and RT afterglow, the room temperatureafterglow profiles of non-codoped and Cu²⁺ codoped LSO:Ce samples weremeasured. See FIG. 10 . A reciprocal correlation between scintillationlight yield and afterglow is found. In the case of the 0.1 at% Cu²⁺codoped sample with improved light yield, afterglow drops by 50%compared to that of the non-codoped sample due to the removal of aVo-associated TL peak at 346 K. Because of the formation of deep trapsassociated with a TL peak at 288 K, the afterglow level of the 0.3 at%Cu²⁺ codoped sample is one order of magnitude higher than that ofnon-codoped LSO:Ce. As seen in the inset of FIG. 10 , the as-grown boulecodoped 0.3 at% Cu²⁺ has a bright blue emission under UV excitation, andthe afterglow emission is still visible after turning off the UVexcitation for one minute.

Summary

High quality 32 mm diameter and 110 mm long LSO:Ce single crystalscodoped with 0.1 and 0.3 at% Cu²⁺ ions were successfully grown by theCzcoralski method. The surface tension of the melt was not reducedenough by Cu²⁺ codoping to affect the crystal growth stability. Unlikethe partial conversion of Ce ions from trivalent to tetravalent by Ca²⁺codoping, Cu²⁺ codoping does not introduce stable Ce⁴⁺ into the LSOlattice. The emission contribution from Ce2 centers gradually reduces asthe Cu²⁺ codoping conentration increases. Despite the fact that Cu²⁺induces an enhanced thermal ionization effect from the Ce³⁺ 5d₁ state,the scintillation yield of LSO:Ce is still improved from 32,000 to39,000 photons/MeV by suppression of Vo defects. Without being bound byany one theory, the shortening of scintillation decay times is regardedas a result of both the enhanced thermal ionization effect from Ce³⁺ 5d₁state and the reduction of the slow Ce2 emission. The similarity incodoping behaviors between Li⁺ and Cu²⁺ in LSO:Ce, and the dissimilarityto codoping behaviors of Ca²⁺ suggest that the empirical selectioncriteria of suitable codopants for performance enhancement in oxidescintillators are not only the valence state of codopant but, also,their ionic radius.

It will be understood that various details of the presently disclosedsubject matter may be changed without departing from the scope of thepresently disclosed subject matter. Furthermore, the foregoingdescription is for the purpose of illustration only, and not for thepurpose of limitation.

1. A scintillator material comprising lutetium oxyorthosilicate (LSO)doped with 0.1 atomic % cerium (Ce) and codoped with 0.3 atomic % copper(Cu).
 2. The scintillator material of claim 1, wherein said material isa single crystal, polycrystalline, or a ceramic material. 3-17.(canceled)
 18. A radiation detector comprising the scintillator materialof claim
 1. 19. The radiation detector of claim 18, wherein the detectoris a medical diagnostic device, a device for oil exploration, and/or adevice for container, vehicle, human, animal, or baggage scanning. 20.The radiation detector of claim 18, wherein the medical diagnosticdevice is a positron emission tomography (PET) device, a single photonemission computed tomography (SPECT) device or a planar nuclear medicalimaging device.
 21. A method of detecting gamma rays, X-rays, cosmicrays, and particles having an energy of 1 keV or greater, the methodcomprising using the radiation detector of claim
 18. 22-28. (canceled)29. A method of altering one or more scintillation and/or opticalproperties of a lutetium oxyorthosilicate (LSO), the method comprisingpreparing the scintillator in the presence of a Ce dopant ion and acodopant ion, wherein the codopant ion is a Cu ion present at 0.3 atomic% , and wherein preparing the scintillator in the presence of the Cedopant ion and the codopant ion provides a scintillator with decreasedscintillation decay time as compared to a scintillator prepared in thepresence of the dopant ion and in the absence of the codopant ion.30-32. (canceled)